Ground Temperature Monitoring During the Period 2004–2024 Indicates Permafrost Degradation in the Austrian Alps

ABSTRACT Long‐term time series on changes in the cryosphere are becoming increasingly important. This study presents data from 20 years of ground temperature monitoring from the eastern‐most confirmed permafrost site in the European Alps (Hochreichart, Austria) spanning the period 2004–2024. Data from eight ground temperature and three air temperature monitoring sites collected in the summit region and a nearby cirque were used. Results at the summit area reveal mean annual temperatures of about 0°C near the surface and of −1.2°C at 2.5 m depths in blocky sediments. Despite strong interannual temperature fluctuations, a warming trend can be seen in all datasets. In most cases, statistically significant changes in annual, seasonal, and even monthly values could only be detected at sites with a continuous dataset of at least 15 years. Ground temperatures increased on average by +0.7°C/dec to 1.0°C/dec, which is consistent with other studies. The number of thawing degree days changed by +150°days/dec to +160°days/dec, whereas the one of freezing degree days by −200°days/dec to ‐210°days/dec. Winter and summer seasons show significant warming trends (by 0.5°C/dec to 1.1°C/dec), while spring and autumn are less clear. At a monitoring site with a continuous record over 20 years, significant monthly warming occurred only in four (February, March, June, August) out of 12 months, with warming rates of 1.6°C/dec (June) to 2.0°C/dec (March). It is shown that a technically simpler ground temperature monitoring network such as the one in the Hochreichart area can provide in some cases more meaningful results than deep‐borehole sites, which are technically more complex and more susceptible to disturbances.